This invention relates generally to earth-orbiting communication satellites and, more particularly, to techniques for testing communication satellites. Typically, communication satellites have multiple independent communication channels, each of which is subject to the introduction of data errors due to faulty components or unwanted signals impressed on the channel. There are basically two ways to test a communication channel: by measuring bit error rates when the channel is carrying selected digital data, and by measuring the channel's response to the introduction of an analog signal.
Prior to this invention, analog or frequency domain testing has been performed by electrical ground support equipment (EGSE) prior to launch of the satellite, and has imposed a significant burden in terms of additional cost and weight. EGSE testing has required the use of multiple test points in the communication system, to make electrical connection with each communication channel. For example, in a 64-channel satellite, an equal number of couplers, attenuators and associated cables are required. The nature of the integration and test procedure is such that, as a practical matter, these additional components must be carried with the satellite into orbit, even though they are only used during testing on the ground. Although bit error rate testing may be performed while the satellite is in orbit, bit error rate testing does not provide a complete and accurate measure of channel quality and cannot reliably predict communication channel errors.
Accordingly, there is a significant need for a technique that allows frequency domain testing of communication satellites, preferably while the satellites are in orbit. The present invention satisfies this need.